The present invention relates generally to wireless communication systems. More particularly, the present invention relates to the maintenance of wireless system data in a wireless terminal.
In a wireless communication system, certain operating parameters of a mobile wireless terminal (e.g. wireless telephone) depend on the location of the wireless terminal. These location dependent operating parameters change as the wireless terminal changes location.
In a wireless cellular system, the overall geographic area which is serviced by a service provider is divided into a plurality of regions, called cells. Each cell has equipment which allows the wireless terminals operating within the cell to communicate with the wireless system. This equipment generally includes one or more antennas connected to radio equipment, and processing hardware for controlling the equipment. Such equipment is well known in the art and will be referred to herein as a base station or cell site.
In a digital cellular system, each cell is assigned a digital control channel (DCCH) which is used to communicate control information between wireless terminals operating within the cell and the cell""s base station. In addition, each cell is assigned a number of voice channels which are used for voice communications by the wireless terminals operating within the cell. The DCCH is used to page a wireless terminal when an incoming call is received and to allow the wireless terminal to signal to the base station that the wireless terminal desires to initiate an outgoing call. The DCCH is also used to set up a call by notifying the wireless terminal of the voice channel assigned to a particular call. The DCCH is a location dependent operating parameter because the DCCH used by a wireless terminal will change as the location of the wireless terminal changes.
Currently, a wireless terminal must continuously monitor the DCCH, and when the signal strength of the DCCH falls below a threshold, the wireless terminal scans the frequency band for another stronger DCCH signal. Generally, the DCCH frequencies are not known to the wireless terminal, which requires that the wireless terminal scan the entire frequency spectrum of the wireless system in order to find a new DCCH. When the strongest DCCH signal is determined, the wireless terminal uses this DCCH for subsequent control communication with the cellular system (i.e., the wireless terminal xe2x80x9ccamps onxe2x80x9d to the new DCCH). This process of changing DCCHs is called reselection. Reselection is similar to the wireless communication technique of a handoff, but handoff refers to changing voice channels during an existing call, while reselection refers to camping on to a new DCCH when there is no active call.
Thus, during operation, a wireless terminal must continuously monitor the DCCH to determine when its signal strength falls below a threshold, and then scan the frequency spectrum for a new DCCH to camp on to. One problem is that the reselection process (i.e., monitoring of the current DCCH signal and the subsequent scanning and camping on) requires that the radio equipment within the wireless terminal remain active. This tends to drain the battery and reduces the operation time that a wireless terminal receives with a given battery.
Another location dependent operating parameter is the identification of the serving mobile switching center (MSC). As is well known, the multiple base stations in a geographic region are connected to one or more MSCs. The MSC controls the overall operation of the wireless communication system, including the overall operation of the base stations connected to the MSC. For purposes of this description, it will be assumed that the multiple base stations within a geographic service area are connected to, and controlled by, a single MSC. It is further assumed that each MSC is associated with a single service provider. Thus, while a wireless terminal moves about within a particular geographic area, it may switch between serving base stations, but it will be receiving service from a single MSC. However, when the wireless terminal travels outside the geographic area served by the MSC, it may enter another geographic area served by another MSC and another service provider. This situation is known as roaming.
As is well known, in order for a roaming wireless terminal to obtain service, the wireless terminal must register with an MSC to set up what is called a visitor location register (VLR) in the MSC. The VLR is an entry in the memory of the MSC which contains a profile of the wireless terminal and which indicates to the MSC that the wireless terminal may operate in the geographic area served by the MSC. In current systems, the DCCH transmits an identification associated with the MSC, called the MSCID. Thus, when a wireless terminal camps on to a DCCH which is transmitting a new MSC identification, the wireless terminal knows that it is roaming and that it must register with the new MSC. A problem similar to the problem described above arises in the roaming context. The wireless terminal must continually scan the DCCH to determine when it is roaming and when it needs to re-register with a new MSC. Again, this continuous scanning and registering tends to drain the battery and reduces the operation time that a wireless terminal receives with a given battery.
One known technique for addressing these problems is to use location information to control certain operating parameters of the wireless terminal. The location information may be supplied, for example, by a global positioning satellite (GPS) receiver in the wireless terminal, or by other location measurement techniques (e.g. triangulation based on signal strengths, dead reckoning). Such techniques are described in the following U.S. Pat. Nos. 5,442,805; 5,678,182; and 5,857,155. One problem with these techniques is that they rely on predetermined locations being programmed into the wireless terminal. Thus, for example, geographic data and associated wireless terminal operating parameters are pre-programmed into the wireless terminals so that the wireless terminals know what operating parameters to use when operating in a pre-programmed location. The scheme utilized in these techniques is not flexible because the location information and operating parameter information must be pre-programmed into the wireless terminal. Thus, as location and parameter information changes, the stored data in each wireless terminal must also change. Further, these techniques may only be used in geographic areas for which data has been pre-stored into the wireless terminal. If the wireless terminal travels to a geographic location for which location and operating parameter data is not already pre-stored in the wireless terminal, these techniques will not work.
The present invention solves the problems of the prior art by dynamically maintaining location dependent operating parameters in a wireless communication terminal.
In accordance with an embodiment of the invention, the wireless terminal dynamically maintains, in a memory of the wireless terminal, a list of previous locations and associated location dependent operating parameters. The wireless terminal periodically determines its current location and then determines whether the current location is within a predetermined distance from a previously stored location. If the current location is within the predetermined distance from the previously stored location, then a determination is made that the location dependent operating parameter stored in association with the previously stored location is appropriate for use in the current location, and the previous location along with its associated location dependent operating parameter, is stored in a predetermined memory location in the wireless terminal. Alternatively, if the current location is not within the predetermined distance from the previously stored location, then the wireless terminal generates a new location dependent operating parameter for its current location and stores the current location and new location dependent operating parameter in the predetermined memory location.
In this manner, the predetermined memory location contains the operating parameter appropriate for use in the current location of the wireless terminal. In one embodiment, the wireless terminal stores locations and associated location dependent operating parameters in a location/parameter table stored in memory, and the predetermined memory location is the first entry of the table. As the wireless terminal moves, new locations and parameters are stored in the first entry of the table with the remaining table entries being shifted down. As such, when the wireless terminal needs to use the location dependent operating parameter, it is readily available to the wireless terminal in the first entry of the table.
In one advantageous embodiment, the location dependent operating parameter is the digital control channel. Thus, in operation in this embodiment, the wireless terminal will be in a low power-consuming sleep mode and will wake up periodically to determine its current location and update its location/parameter table if necessary. When a wireless terminal needs to place a call using the DCCH, or monitor for an incoming call page using the DCCH, the appropriate DCCH for the wireless terminal""s current location is immediately available to the wireless terminal in the first entry of the location/parameter table.
In accordance with another embodiment, the invention is used to improve the roaming capability of a wireless terminal. In this embodiment, the location dependent operating parameter is the MSCID. Again, the wireless terminal remains in a low power consuming sleep mode and wakes up periodically to determine its current location and update its location/parameter table with the MSCID of the current serving MSC if necessary. In this embodiment, if the first entry of the location/parameter table needs to be updated with a new MSCID, then the wireless terminal will also re-register with the new MSC identified by the MSCID. Thus, the wireless terminal remains registered with the appropriate MSC so that it may obtain service from the MSC.
In accordance with one advantage of the invention, the wireless terminal dynamically maintains location dependent operating parameters while conserving battery power. The wireless terminal may operate in a low power-consuming sleep mode and only wake up periodically in order to perform a current location determination, and then update its location dependent operating parameters only if necessary. The principles of the invention allow for the maintenance of location dependent parameter data without the need for predetermined locations and associated operating parameters being pre-programmed into the wireless terminal.
These and other advantages of the invention will be apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying drawings.